25 April WHO declares public health emergency of international concern as result of 7 cases of Swine Influenza A/H1N1 in USA

26 April 20 cases to date confirmed in USA, 18 cases to date Mexico. Many more cases suspected but there is a lag of several days for full confirmatory tests to be done and Mexican confirmations have to be done in Canada due to USA biosecurity rules.

3 July 89921 cases with 382 deaths reported to WHO or 90852 cases with 384 deaths reported to ECDC

16 July WHO reports "In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less than six weeks". 128,273 cases with 679 deaths reported to ECDC. However in one reporting country with good community surveillance, the UK, 55,000 new cases estimated in last week when only 10,649 confirmed including 29 deaths in that week (and only 17 of those deaths in the report to ECDC figure)

6 August 2010 WHO reports 18,449 deaths had been notified worldwide with 491,382 cases notified as serology positive[3] The pandemic phase ended officially on 10th August 2010[4].

The plot above starts on 15th April 2009 and from July shows increasingly incomplete data as reporting changed. UK suspected data was not published from 15/6/09 and from 17/6/09 clinically presumed cases presumably diagnosed in retrospect by resolved symptoms were reported. From 25/6/09 Scotland stopped reporting clinically presumed cases. UK data was no longer issued on a daily basis on from 2/7/09 but case ascertainment was probably fair up until the second week of June at least and is likely to be as good data as any other nation could offer at close to real time. Issues such as case ascertainment policies, resources to do this and use of virus detection verus antibody detection mean that this data simply gives a feel for what was really happening. For example UK and Australia by the beginning of July were reporting very similar numbers of confirmed cases but the Australian number of deaths were 3 times higher from effectively identical start times. The most likely explanation is better initial case ascertainment in the UK due mainly to seasonal factors forcing Australia to move to the mitigation and treatment phase much sooner than the UK. The death rate is probably lower than 1 per 1000 infected with fully functioning health care systems in the first epidemic wave but is more than 0.5 per 1000. While unexceptional death rates for a epidemic it as atypical as it is much more biased towards younger adults than seasonal influenza and is certainly the fastest spreading pandemic in history by an order of magnitude. The excess mortality of the 1918 (second wave) pandemic might only be three times greater assuming only half the population were infected then[5]. There is nothing particularly reassuring in the data to hand compared to say the 1957/58 pandemic as already by July southern hemisphere countries are noting heavier demands on their health systems than normal in recent years for seasonal influenza[6]. In the graph above UK data is additively displayed, but in graph below UK data is shown non-additively to illustrate the problems with suspected cases and publicity bias. WHO stopped consistent daily updates on 30/5/09 and ECDC figures were increasingly used after this date. The ECDC has analysed the early European data by date of onset and there are two distinct phases, the first associated with travelers returning from Mexico peaking about 27th April and almost disappearing in second week of May. The second was associated with travel to the USA which really started in 3rd week of May, and these imported cases peaked in the first few days of June and then internal secondary transmission cases became more dominant.

The plots below show time course from 1st March 2009 to 1st June 2009

The data below shows incident data from Mexico first wave. At the peak of the outbreak, about 27th April there were about 1300 new probable cases a day, never confirmed or excluded known to the authorities and an additional 385 confirmed cases as shown occurred that day (data up to 2nd June, will increase slightly as later tests come in). The data displayed in the last few days of May is definitely incomplete and likely to increase from 2 cases to over ten/day.